1896.] G. S. A. Ranking — A Note on Indigo Manufacture. 55 



used to macerate the Indigo plant, the application of heat during 

 maceration (" steeping "), and last but not least prolonged "beating" 

 in order to oxidise imperfectly fermented Vat-liquor, all result in the 

 formation of the soluble Indigo-brown and should therefore be avoided 

 in manufacture. 



The gases evolved during fermentation I have found to be principal- 

 ly Carbon dioxide and Nitrogen in the following proportions C0 2 = 31 

 per cent. N = 62 per cent. Hydrogen forms a very small proportion of 

 the evolved gases, only 6*75 per cent. 



Marsh gas also seems to be very sparingly generated during fer- 

 mentation of Indigo. I propose to extend my observations on the 

 evolved gases at some future opportunity. 



